Over the last several decades data center servers have typically been cooled by means of non-centralized air conditioning units, referred to as Computer Room Air Conditioning (CRAC) units, located inside or adjacent to the data center. Some cooling system designs have used centralized constant volume Air Handling Units (AHUs).
Furthermore, the cooling load densities (W/m2) for data centers have increased substantially in line with Moore's law relating to computer chip density increase. This has led to data centers having a very high usage of energy, per surface area, in the order of at least 10 times that of typical office air conditioning applications.
To realize increased data center energy efficiency requires improvements in air management. Optimum air management requires physical segregation of hot and cold air streams and dynamically matching the supply air volume of the cooling systems (CRAC units or AHUs) with the variable demand air volume of the servers.
Whereas air free cooling is standard in Variable Air Volume (VAV) Air Handling Unit (AHU) systems used for large office air conditioning applications, it is not applied to data centers.
Data center high-density requirements have identified inefficiencies in traditional data center designs: air bypass and recirculation. Bypass is airflow supplied by the cooling units that directly returns to the cooling units without cooling the servers. Recirculation airflow is warm air discharged from a server that is delivered directly into the same or another server's air inlet without being cooled. Air management in data centers in an attempt to resolve bypass and recirculation have been addressed by vendors with packaged solutions that cool the air close to the heat source (i.e., the servers).
If air management issues of recirculation were solved, air could be supplied at higher temperatures, e.g., 22° C. to 25° C. rather than at approximately 12° C. to 15° C. (i.e., around 10K (i.e., Kelvin) lower). This potentially saves energy in the refrigeration systems, as the evaporator temperature of the refrigeration systems can be set higher.
If air management issues of bypass were solved, less air could be supplied, hence saving fan energy. Modern servers (i.e., blade type) have variable air volume controlled by a variety of internal sensors.
The design ΔT (“delta T”) (airflow), wherein T represents temperature, of a typical server is 15K, but minimum load and flow rates are such that the minimum delta T is around 7K.
As a result of the in server load densities, in line with Moore's law, manufacturers are increasing loads on chips, using the same air flow rates, which will, or is predicted to, result in a future design delta T of 25K, or more. At full load, a data center could potentially require air at 25° C. and discharge it at approximately 40° C. to 50° C. (e.g., 25° C.+15K or 25K).
Given that air temperatures in many worldwide locations (e.g., United Kingdom) very seldom exceed 30° C., there are significant energy savings if air free cooling were to be used. Mechanical cooling (supplemental cooling) would only be necessary to cool air from outdoor conditions to design supply conditions, rather than from the higher return/exhaust air temperature from the servers.
In view of the foregoing, a need exists to overcome one or more of the deficiencies in the related art.